The commercialization of organic-inorganic hybrid perovskite light-absorber material has been hampered by factors such as environmental stability, substandard interface and defects. Focus has shifted to the single-crystalline perovskite which is believed to be defect free, has better stability, longer carrier lifetime and diffusion length, wider optical absorption spectrum, and lower trap-state-density.
Professor Shengzhong (Frank) Liu and colleagues have successfully used a dynamic flow microreactor system to grow geometry-controlled ultrathin single crystalline perovskite wafers of different ranges of thicknesses. Their work is published in Advanced Materials, 2016, 28, 9204-9209; Adv. Opt. Mater. 2016, 4 (11), 1829-1837; Sci. China Chem. 2017, DOI:10.1007/s11426-017-9081-3.
The authors employed a dynamic-flow reaction system. They used 2 spacers to separate and align 2 thin glass slides so as to limit the crystal growth to a slit channel. A peristaltic pump was used to achieve dynamic flow of the precursor solution.
The research team fabricated single crystalline wafers of approximately 150, 330, 670, and 1440 mm in thickness, which showed that the crystal growth was confined within the microreactor.
The authors observed no obvious grain boundaries and cracks from the scanning electron microscopy examination, indicating that the wafer is of high single-crystalline quality throughout. The mapping analysis and line scan results of the scanning electron microscopy energy-dispersive x-ray spectroscopy show an even distribution as well as consistency in atomic ratio of carbon, nitrogen, lead, and iodine constituents of the produced wafer.
When the single crystalline perovskite wafer is compared with the microcrystalline thin films in UV-Vis-NIR spectrophotometry, the authors observed that the former displayed a significant red-shifted light absorption edge at 900 nm as compared with 800 nmfor the latter, a significant advantage for PV and optoelectronic applications.
From the thermogravimetric analysis, the single crystalline wafer is similar to bulk single crystals in thermal decomposition, exhibiting stability at higher temperatures over the microcrystalline films.
The authors designed a hole only device to analyze the trap density of the single crystalline wafer by testing, at different biases, the evolution of space-charge-limited current. The trap density of both the single crystalline wafer and the large single crystals was found to be similar. The Hall effect is also similar for both the single crystalline wafer and the single large crystals.
To simulate an optoelectronic device, the team designed 100 photodetectors on the perovskite wafer, which demonstrated the feasibility of integrated circuits being mass produced on these wafers. At different bias voltages and illumination, the authors observed that at a 2V bias the photocurrent in the wafer was approximately 700 µA, while this was limited to only 2 µA for the microcrystalline thin films which is approximately 350 times smaller. The single crystalline wafer detector showed significant response at 880 nm while the microcrystalline thin film device shows no response at all, which confirmed that the former has a broader optical absorption than the latter.
Yucheng Liu, Yunxia Zhang, Zhou Yang, Dong Yang, Xiaodong Ren, Liuqing Pang, and Shengzhong(Frank) Liu. Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices. Advanced Materials, 2016, 28, 9204-9209.Go To Advanced Materials